Not allowing signs is one thing. Trespassing on property to remove/steal your sign is another. I doubt the covenants give them that authority. lol The usual process would be to contact the offending property owner, inform them they are in violation, and tell them to remove the sign. Few things are more aggravating than an overzealous HOA officer who thinks they are the gestapo.
Having said that, it's possible that your property could be subject to the HOA regs even if your ownership predated the association, but that's a question you should direct to an attorney who can do a title exam and give you an opinion. But before you go that route, _try_ to work with the HOA. Find out how properties are typically marketed in that development. You just might decide that is the most effective way to market the property.